Add (guix build-system perl).

* guix/build-system/perl.scm, guix/build/perl-build-system.scm: New files.
* Makefile.am (MODULES): Add them.
* guix/build-system/gnu.scm (standard-inputs): Make public.

guix/build/perl-build-system.scm

@@ -0,0 +1,61 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build perl-build-system)
+  #:use-module ((guix build gnu-build-system)
+                #:renamer (symbol-prefix-proc 'gnu:))
+  #:use-module (guix build utils)
+  #:use-module (ice-9 match)
+  #:export (%standard-phases
+            perl-build))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard Perl package build procedure.
+;;
+;; Code:
+
+(define* (configure #:key outputs (make-maker-flags '())
+                    #:allow-other-keys)
+  "Configure the given Perl package."
+  (let ((out (assoc-ref outputs "out")))
+    (if (file-exists? "Makefile.PL")
+        (let ((args `("Makefile.PL" ,(string-append "PREFIX=" out)
+                      "INSTALLDIRS=site" ,@make-maker-flags)))
+          (format #t "running `perl' with arguments ~s~%" args)
+          (zero? (apply system* "perl" args)))
+        (error "no Makefile.PL found"))))
+
+(define %standard-phases
+  ;; Everything is as with the GNU Build System except for the `configure'
+  ;; phase.
+  (alist-replace 'configure configure
+                 gnu:%standard-phases))
+
+(define* (perl-build #:key inputs (phases %standard-phases)
+                     #:allow-other-keys #:rest args)
+  "Build the given Perl package, applying all of PHASES in order."
+  (set-path-environment-variable "PERL5LIB" '("lib/perl5/site_perl")
+                                 (match inputs
+                                   (((_ . path) ...)
+                                    path)))
+  (apply gnu:gnu-build
+         #:inputs inputs #:phases phases
+         args))
+
+;;; perl-build-system.scm ends here